1. Field of the Invention
The present invention is in the field of night vision devices of the light amplification type. More particularly, the present invention relates to an improved night vision device having an image intensifier tube (I.sup.2 T) which serves as a detector for the reflected portion of a laser light pulse which is utilized to effect laser range finding. Thus, the present invention is also in the field of laser range finders. Particularly, the present invention relates to a night vision device and laser range finder using magnetic coupling of an electrical response caused by the reflected portion of a laser light pulse to a oscillator circuit utilizing phase matching or phase difference detection, for example, to provide an electrical output response. A method of operating the night vision device and a method of laser range finding (LRF) are disclosed also.
2. Related Technology
Laser range finders have been known for a considerable time. These devices are used, for example, by surveyors to calculate the distance from a point of observation to an object such as a geological formation in the field of view (i.e., the device requires line of sight relationship between a user and the object to be ranged). Generally, a laser range finder operates by projecting a pulse of laser light at an object. The laser light illuminates the object, and a portion of the laser light is reflected back toward the laser range finder device. The reflected laser light is detected, and the time interval required for the laser light pulse to travel to and from the object is measured. From this time interval measurement and the known speed of light, the distance between the laser range finder and the object is calculated.
A conventional laser range finder of the type described above generally includes a laser capable of producing laser light pulses of high peak power and very short duration (i.e., less than 50 ns duration). The detector for the reflected laser light may include a high speed photodetector (such as an InGaAs avalanche photodiode), which is coupled to a high gain, high speed amplifier. A high speed digital counter may be used as a timer to determine the time interval required for the laser light to travel to the object and for laser light reflecting off of the object to travel back to the device. From this time interval information an internal electronic calculator determines the range to the object, and this range is presented to the user of the device, usually on a visual display screen.
These conventional laser range finders have the disadvantage of a considerable cost and complexity. The laser pulses must be of considerable intensity as well, which requires a high power laser. The conventional laser range finders are subject to optical and electrical problems, such as vulnerability to electromagnetic interference, damage to electrical components and damage to optical components. Reliability of the devices is also adversely impacted by their complexity.
On the other hand, conventional night vision devices of the image intensification type (i.e., light amplification) type have also been known for a considerable time. Generally, these night vision devices include an objective lens which focuses invisible infrared light from the night time scene onto the transparent light-receiving face of an image intensifier tube. At its opposite image-face, the image intensifier tube provides an image in visible yellow-green phosphorescent light, which is then presented to a user of the device via an eye piece lens.
Even on a night which is too dark for natural human vision to allow a person to see well, invisible infrared light is richly provided by the stars in the night time sky. Human vision can not utilize this infrared light from the stars because the so-called near-infrared portion of the spectrum is invisible for humans. A night vision device of the light amplification type can provide a visible image replicating the night time scene.
A contemporary night vision device will generally use an image intensifier tube with a photocathode behind the light-receiving face of the tube. The photocathode is responsive to photons of infrared light to liberate photoelectrons. These photoelectrons are moved by a prevailing electrostatic field to a microchannel plate (MCP) having a great multitude of dynodes, or microchannels with an interior surface substantially defined by a material having a high coefficient of secondary electron emissivity. The photoelectrons entering the microchannels cause a cascade of secondary emission electrons to move along the microchannels so that a spatial output pattern of electrons which replicates an input pattern, and at a considerably higher electron density than the input pattern results. This pattern of electrons is moved from the microchannel plate to a phosphorescent screen to produce a visible image. A power supply for the image intensifier tube provides the electrostatic field potentials referred to above, and also provides a field and current flow to the microchannel plate.
Conventional night vision devices which are usable to sight a weapon are found in U.S. Pat. No. 5,084,780; and 5,035,472. Neither of these patents is believed to suggest or disclose a night vision device which is combined with a laser range finder using the image intensifier tube of the night vision device as a detector for laser light in the laser range finder. Further, no conventional technology known to the Applicant utilizes magnetic coupling of an electrical response signal created in the image intensifier tube by the reflected portion of a laser light pulse into an electrical detector circuit utilizing an reference oscillator and responding to, for example, a resulting phase difference or phase matching of the reference oscillator with a signal oscillator.